Group javascript array object by same key

by

You could take a Map and reduce the array by adding the value to the month nad get new arrays from the grouped result.

var data = [{ month: 'Jan', value: 3 }, { month: 'Jan', value: 3.5 }, { month: 'Feb', value: 2.1 }, { month: 'Mar', value: 6 }, { month: 'Apr', value: 4.3 }, { month: 'May', value: 5.5 }, { month: 'Jun', value: 7 }, { month: 'Jun', value: 9 }, { month: 'Jul', value: 7 }, { month: 'Jul', value: 9 }, { month: 'Jul', value: 7 }, { month: 'Aug', value: 9 }, { month: 'Sep', value: 9 }, { month: 'Sep', value: 9 }, { month: 'Oct', value: 8 }, { month: 'Oct', value: 5 }, { month: 'Oct', value: 3 }, { month: 'Nov', value: 12 }, { month: 'Nov', value: 19.5 }],
    result = Array.from(
        data.reduce(
            (m, { month, value }) => m.set(month, (m.get(month) || 0) + value),
            new Map
        ),
        ([month, value]) => ({ month, value })
    );

console.log(result);
.as-console-wrapper { max-height: 100% !important; top: 0; }

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